Power-down means in integrated circuit devices is a feature for reducing an item such as power consumption or electro-magnetic radiation by disabling the circuit in the device. The circuit is kept disabled as long as a pre-determined power-down condition prevails. When the power-down condition is removed, the circuit is re-enabled.
For example, a memory circuit chip powers down when the CE signal (chip enable) is negated and powers back up again when the CE signal is reasserted. Toshiba MOS Memory Products 1989 Databook, page D.3, shows a memory chip that is powered down in response to a fixed combination of values of CE.sub.1 and CE.sub.2 signals. Note that the prior art shows a predetermined character of the input signals required to trigger the powering down of the circuit. This predetermined character or fixed combination is built into the device during manufacturing.